OFFSHORE SECURITIES SUBSCRIPTION AGREEMENT
This Offshore Securities Subscription Agreement ("Agreement") is executed in reliance upon the transaction
exemption afforded by Regulation S ("Regulation S") as promulgated by the Securities and Exchange
Commission ("SEC"), under the Securities Act of 1933, as amended ("1933 Act").
This Agreement has been executed by the undersigned in connection with the private placement of 7%
Convertible Debentures (hereinafter referred to as the "Debentures") of ImmunoGen, Inc., a corporation
organized and existing under the laws of the Commonwealth of Massachusetts, U.S.A., NASDAQ National
Market Symbol "IMGN" (hereinafter referred to as the "COMPANY"). The Debentures being sold pursuant to
this Agreement, and the Shares (as defined below), have not been registered under the 1933 Act and may not be
offered or sold in the United States or to U.S. Persons, other than distributors (as such terms are defined in
Regulation S), unless the Debentures or the Shares, as the case may be, are registered under the 1933 Act, or an
exemption from the registration provisions of the 1933 Act is available. The terms on which the Debentures may
be converted into common stock (the "Shares") and the other terms of the Debentures are set forth in the pro
forma Debenture in Annex I annexed hereto. This subscription and, if accepted by the COMPANY, the offer
and sale of Debentures and the Shares issuable upon conversion thereof (collectively the "Securities"), are being
made in reliance upon the provisions of Regulation S ("Regulation S") under the 1933 Act.
if applicable, a [Corporation][Partnership][Trust] organized under the laws of __________, a non USA
jurisdiction (hereinafter referred to as the "PURCHASER") hereby represents and warrants to, and agrees with,
the COMPANY as follows:
1. Agreement to Subscribe.
a. Subscription Amount. The undersigned hereby subscribes for $______________ in principal amount of 7